This invention relates to a method and system for controlling the capacity or delivery quantity of a variable capacity wobble plate compressor adapted for compressing refrigerant gas recirculated in air conditioning systems for automotive vehicles.
Conventionally, a variable capacity wobble plate compressor has been known which is equipped with an electromagnetic valve for opening and closing a passage communicating a suction chamber with a crankcase, and arranged such that the degree of communication between the suction chamber and the crankcase is controlled through control of the opening degree of the electromagnetic valve to vary the pressure in the crankcase, whereby the angularity of a wobble plate is varied to change the stroke of pistons to thereby vary the capacity or delivery quantity. However, according to the compressor constructed as above, the opening control of the electromagnetic valve is conducted in response only to the output from a humanly operated temperature setting device. However, in actuality, the suction pressure varies with a change in the thermal load and there occurs a pressure loss (as a function of the flow rate of refrigerant) between the outlet of the evaporator and the inlet of the compressor, so that the evaporator is frozen and, as a result, a required cooling rate is not obtained.
When the thermal load varies, the suction pressure also varies accompanying a change in the evaporator boiling pressure whereby the desired evaporator boiling pressure may not be obtained. The evaporator boiling temperature changes with the evaporator boiling pressure, so that, for example, when the thermal load decreases the evaporator freezes, and, on the other hand, when the thermal load increases the required cooling performance cannot be obtained.